Portable pneumatic tools such as pneumatic fastening tools, metal piercing tools and crimping tools each require a source of compressed air. Currently, almost all portable pneumatic tools rely upon external air compressors to deliver compressed air via a flexible compressed air hose. External air compressors are typically either shop models or portable models.
Shop air compressors are large, heavy compressors which are often fixed in place and not designed to be frequently moved from one work site to another. An immovable shop air compressor and compressed air hose of finite length limit the ability to take the portable pneumatic tool to where the work is to be performed. The portable pneumatic tool is, in effect, tethered to the fixed shop air compressor and its portability is thereby reduced.
In contrast, portable air compressors do have the ability to be transported from one work site to another. Still, they remain relatively heavy or bulky and awkward to transport—requiring time and manpower to move around the worksite. As with shop models, portable air compressors require a hose to bring the compressed air from the compressor to the tool. Because of the need for a compressed air hose, the portable pneumatic tool remains tethered to the portable air compressor. When the portable air compressor cannot be easily moved around the worksite, the portability of the portable pneumatic tool tethered to the compressor is in turn limited. The lightest and most portable of the portable air compressors are powered by an electric motor. However, these electric powered models then require access to an external electrical power source which is an additional limitation to the portable compressor's portability.
Additionally, portable air compressors having sufficient capacity to power pneumatic tools may use induction motors or series wound AC motors known as universal motors. Induction motors are big, heavy and expensive but can be directly coupled to the compressor or pump. This eliminates the need to couple the motor to the compressor with gears or a belt(s). Series wound AC motors are smaller, lighter and less expensive. However, they are not as efficient as induction motors and in particular, produce low power density at low speeds. They must thus be coupled to the compressor by gears or a belt with a sufficient reduction ratio so that the motor can be run at high speeds to achieve high power densities.
Further, with either class of external air compressor-shop or portable models—the required purchase of the external air compressor to accompany the portable pneumatic tool is an additional expense which can be difficult to bear for some consumers, especially if the external air compressor will serve no other purpose than to power the portable pneumatic tool.
Also, with either class of external air compressor, a hose is required to deliver the compressed air from the external air compressor to the tool. The hose can get in the way of using the tool, can be time consuming to connect and disconnect, adds additional weight that must be carried from one work site to another, and can even be a safety hazard. The hose and required fittings are also an additional expense to the user and will eventually require maintenance or replacement.
Thus, as can be easily seen, the dependence of portable pneumatic tools upon external air compressors limits the portability of these tools, imposes additional costs and reduces their utility.
The utility of a hand-held pneumatic fastening tool, one type of portable pneumatic tool, is particularly affected by its dependence upon an external air compressor. Hand-held pneumatic fastening tools are designed to be quickly carried by hand to where a fastener is to be driven into a workpiece. As explained above, an external air compressor connected to the tool at a minimum complicates moving the hand-held pneumatic fastening tool around the work site. Also, the hose protruding from the tool can get in the way of the work to be done, and can restrict the use of the tool in confined spaces or difficult to reach places. Setup time can also be a problem. Especially when only a few fasteners are to be driven, the time required to setup and connect the external air compressor to the hand-held pneumatic fastening tool is proportionately high to the actual working time of the tool. In some cases, it may take longer to setup the external air compressor than to drive the fastener by hand. In such cases, a user will naturally resort to manually driving the fastener with a hammer.
All of the above-mentioned problems could be overcome if the portable pneumatic tool's dependence upon an external air compressor was eliminated. In the field of hand-held fastening tools, cordless, combustion-based fastening tools have been proposed and produced. One well known type of combustion-based fastening tool uses an internal combustion chamber in lieu of an external air compressor. A combustible gas and air mix in a combustion chamber in these tools. A spark plug ignites this combustible mixture to create pressure that works on a piston to drive the fastener.
While eliminating the dependence upon an external air compressor, these combustion-based fastening tools exhibit other problems. For example, these combustion-based tools require the recurring purchase of proprietary fuel cells available from the tool's manufacturer. One tool's fuel cells typically cannot be used in the tools of another manufacturer. Maintenance can also be a problem. Some of these combustion-based tools require disassembly after every 30,000 or so shots to clean the residue of the combustion. Further, the design and construction of these combustion-based fastening tools differs substantially from other hand-held pneumatic fastening tools resulting in a substantial lack of part interchangeability. Finally, these combustion-based fastening tools cannot be both a cordless fastening tool and a hand-held pneumatic fastening tool relying upon an external air compressor. The ability to be selectively powered by combustion or external compressed air would increase the adaptability of the tool.
U.S. Pat. No. 3,150,488 to Haley, U.S. Pat. No. 4,215,808 to Sollberger et al., and U.S. Pat. No. 5,720,423 to Kondo et al. each propose a hand-held fastening tool which does not rely upon an external air compressor and is not combustion-based.
The Haley patent discloses a fastening tool with a pump. The pump pumps a non-compressible fluid which forces a drive piston rearward in a cylinder. The retraction of the drive piston in turn compresses air in an accumulator. Pulling a trigger switch on the fastening tool activates the pump. At some time after the pump has been running and the air has been compressed in the accumulator, the drive piston reaches the limit of its rearward movement. This causes the separation of the drive piston from an accumulator piston, which in turn allows the compressed air to act on the drive piston. The compressed air drives the drive piston forward to drive the fastener.
The Sollberger et al. and Kondo et al. patents each disclose similar proposed fastening tools. In each of these proposed fastening tools, an electric motor drives a piston rearward in a cylinder through an arrangement of gears and linkages. Pulling the trigger on these tools causes the electric motor to be energized to move the piston rearward in the cylinder. As the piston moves rearward, the air behind the piston which is trapped in the cylinder is compressed. At a certain point, the piston is freed from the driving force of the motor and is rapidly propelled forward in the cylinder by the force of the compressed air trapped behind. As the piston is propelled forward, it strikes and drives the fastener.
In these three patents, each of the proposed designs does eliminate the hand-held fastening tool's dependence upon an external air compressor. However, each of the proposed designs would result in one or more new drawbacks. First, pulling the trigger on each of these fastening tools would not immediately result in the firing of the tool and the driving of the fastener. Rather, pulling the trigger would merely activate the motor or pump which begins the process of compressing the air. Then, after the air has been compressed, a release mechanism would automatically fire the tool and drive the fastener. The lag time between the pulling of the trigger and the firing the tool could be a safety concern. This lag time would also reduce the operating speed of the tool and would make operation of the tool less intuitive for the user.
Second, in these proposed fastening tools the maximum air pressure needed to perform an amount of work on the drive piston sufficient to drive the fastener is much greater than with standard pneumatic fastening tools. The work that the compressed air performs on the drive piston in order to drive the fastener is a result of the compressed air exerting a force on the drive piston as it travels downward in its cylinder. The pressure of the compressed air in a standard pneumatic fastening tool will remain high throughout the drive piston's travel because the compressed air is provided by an external air compressor, which is almost a constant-pressure supply source. In contrast, the pressure of the compressed air in the proposed fastening tools will linearly decrease to zero as the drive piston returns to its start position. Because of the lack of air pressure at the end of the drive piston's travel, there must be a relatively high air pressure at the beginning in order to sufficiently drive the fastener flush with the workpiece.
The necessity for high air pressure in these proposed fastening tools is a disadvantage because compressing the air to such a high pressure is energy inefficient. This can make a difference in the weight of these proposed tools if they are to be powered by batteries. A related effect is that the high pressure could generate a significant amount of heat that must be dissipated. In addition to the reduction in efficiency and increase in heat, holding the high pressure compressed air behind the piston for the relatively long period of time before these proposed fastening tools finally fire will require relatively expensive and possible maintenance-intensive seals around the drive piston.
This need for such high air pressure might be obviated if the air in the cylinder were pre-compressed so that air pressure would be maintained even when the piston is in its start position. While the air in some of the proposed fastening tools in the above patents could be pre-compressed, this would require an additional mechanism onboard the tool to maintain this pressure as the pre-compressed air would inevitably leak out and need recharging.
Third, each of these proposed tools relies upon new and untested mechanisms for compressing the air. These new mechanisms are not present in any present-day hand-held pneumatic fastening tools which rely upon external air compressors. The parts for these new mechanisms, especially initially, will be costly to engineer, design, and produce. Likely, these new mechanisms would not immediately be as reliable as the mature technology embodied in present-day hand-held pneumatic fastening tools.
Thus, while the proposed fastening tools disclosed in the above-described patents would not be reliant upon an external air compressor and would not possess the drawbacks of external air compressors, these proposed tools would suffer other important, and potentially more serious, drawbacks.